Commit e73f8959 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Al Viro
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task_work_add: generic process-context callbacks 



Provide a simple mechanism that allows running code in the (nonatomic)
context of the arbitrary task.

The caller does task_work_add(task, task_work) and this task executes
task_work->func() either from do_notify_resume() or from do_exit().  The
callback can rely on PF_EXITING to detect the latter case.

"struct task_work" can be embedded in another struct, still it has "void
*data" to handle the most common/simple case.

This allows us to kill the ->replacement_session_keyring hack, and
potentially this can have more users.

Performance-wise, this adds 2 "unlikely(!hlist_empty())" checks into
tracehook_notify_resume() and do_exit().  But at the same time we can
remove the "replacement_session_keyring != NULL" checks from
arch/*/signal.c and exit_creds().

Note: task_work_add/task_work_run abuses ->pi_lock.  This is only because
this lock is already used by lookup_pi_state() to synchronize with
do_exit() setting PF_EXITING.  Fortunately the scope of this lock in
task_work.c is really tiny, and the code is unlikely anyway.

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Acked-by: default avatarDavid Howells <dhowells@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Richard Kuo <rkuo@codeaurora.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Alexander Gordeev <agordeev@redhat.com>
Cc: Chris Zankel <chris@zankel.net>
Cc: David Smith <dsmith@redhat.com>
Cc: "Frank Ch. Eigler" <fche@redhat.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Larry Woodman <lwoodman@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 62366c88

include/linux/sched.h

+2 −0
Original line number Diff line number Diff line
@@ -1400,6 +1400,8 @@ struct task_struct { 
	int (*notifier)(void *priv);

	void *notifier_data;

	sigset_t *notifier_mask;

	struct hlist_head task_works;



	struct audit_context *audit_context;

#ifdef CONFIG_AUDITSYSCALL

	uid_t loginuid;

include/linux/task_work.h

0 → 100644
+33 −0
Original line number Diff line number Diff line 
#ifndef _LINUX_TASK_WORK_H

#define _LINUX_TASK_WORK_H



#include <linux/list.h>

#include <linux/sched.h>



struct task_work;

typedef void (*task_work_func_t)(struct task_work *);



struct task_work {

	struct hlist_node hlist;

	task_work_func_t func;

	void *data;

};



static inline void

init_task_work(struct task_work *twork, task_work_func_t func, void *data)

{

	twork->func = func;

	twork->data = data;

}



int task_work_add(struct task_struct *task, struct task_work *twork, bool);

struct task_work *task_work_cancel(struct task_struct *, task_work_func_t);

void task_work_run(void);



static inline void exit_task_work(struct task_struct *task)

{

	if (unlikely(!hlist_empty(&task->task_works)))

		task_work_run();

}



#endif	/* _LINUX_TASK_WORK_H */

include/linux/tracehook.h

+11 −0
Original line number Diff line number Diff line
@@ -49,6 +49,7 @@ 
#include <linux/sched.h>

#include <linux/ptrace.h>

#include <linux/security.h>

#include <linux/task_work.h>

struct linux_binprm;



/*
@@ -164,8 +165,10 @@ static inline void tracehook_signal_handler(int sig, siginfo_t *info, 
 */

static inline void set_notify_resume(struct task_struct *task)

{

#ifdef TIF_NOTIFY_RESUME

	if (!test_and_set_tsk_thread_flag(task, TIF_NOTIFY_RESUME))

		kick_process(task);

#endif

}



/**
@@ -185,6 +188,14 @@ static inline void tracehook_notify_resume(struct pt_regs *regs) 
{

	if (current->replacement_session_keyring)

		key_replace_session_keyring();

	/*

	 * The caller just cleared TIF_NOTIFY_RESUME. This barrier

	 * pairs with task_work_add()->set_notify_resume() after

	 * hlist_add_head(task->task_works);

	 */

	smp_mb__after_clear_bit();

	if (unlikely(!hlist_empty(&current->task_works)))

		task_work_run();

}



#endif	/* <linux/tracehook.h> */

kernel/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -5,7 +5,7 @@ 
obj-y     = fork.o exec_domain.o panic.o printk.o \

	    cpu.o exit.o itimer.o time.o softirq.o resource.o \

	    sysctl.o sysctl_binary.o capability.o ptrace.o timer.o user.o \

	    signal.o sys.o kmod.o workqueue.o pid.o \

	    signal.o sys.o kmod.o workqueue.o pid.o task_work.o \

	    rcupdate.o extable.o params.o posix-timers.o \

	    kthread.o wait.o kfifo.o sys_ni.o posix-cpu-timers.o mutex.o \

	    hrtimer.o rwsem.o nsproxy.o srcu.o semaphore.o \

kernel/exit.c

+4 −1
Original line number Diff line number Diff line
@@ -946,11 +946,14 @@ void do_exit(long code) 
	exit_signals(tsk);  /* sets PF_EXITING */

	/*

	 * tsk->flags are checked in the futex code to protect against

	 * an exiting task cleaning up the robust pi futexes.

	 * an exiting task cleaning up the robust pi futexes, and in

	 * task_work_add() to avoid the race with exit_task_work().

	 */

	smp_mb();

	raw_spin_unlock_wait(&tsk->pi_lock);



	exit_task_work(tsk);



	exit_irq_thread();



	if (unlikely(in_atomic()))

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